The present invention relates to a composite construction made of a sintered body obtained by coating the outer periphery of a core material with a shell layer.
Ceramics and cermets obtained by bonding crystal grains with a bonding phase have hitherto been known. For example, a sintered body obtained by bonding hard particles such as carbides, nitrides, carbonitrides of metals of Groups 4a, 5a and 6a of the Periodic Table, diamonds or cubic boron nitride with an iron group metal is used as cutting tools, mining applications and wear-resistant parts by controlling the contents of the crystal grains having a high hardness and the iron group metal having a high toughness. It has generally been known that, in conventional hard materials described above, the hardness has an inverse proportional relationship relative to the toughness and it is hard to overcome both high hardness and high toughness. Particularly, a polycrystalline diamond (hereinafter, PCD) had a problem such as low chipping resistance when used in cutting tools, although it has high hardness but has low toughness and low impact resistance.
Therefore, there has been studied a technique of improving the toughness, in addition to the hardness and the strength of a construction, by coating the outer periphery of a continuous core material such as fibers with the other materials. For example, Japanese Unexamined Patent Publication (Kokai) No. 11-139884 discloses a ceramic composite obtained by spraying a second phase component over the outer periphery of each core material (linear ceramics), binding plural coated core materials into a bundle in a uniaxial direction, and compressing and sintering the bundle, and thus increasing the fracture resistance of the construction.
Although a composite construction, which is obtained by coating PCD as a core material with a shell material, for example, a sintered alloy such as cemented carbide (WC) containing metals of Groups 4a, 5a and 6a of the Periodic Table as a main component, is proposed, it is not studied about a composition which can overcome both high hardness and high toughness. Furthermore, even if PCD is merely combined with the sintered alloy, cracks and delamination partially occur sometimes at an interface between the core and the shell, which leads to low toughness, because of a large difference in thermal expansion coefficient between diamonds of the core material and hard particles as the main component of the shell layer.
U.S. Pat. No. 6,063,502 discloses that a composite construction is manufactured by coating the outer periphery of a core material made of a high hardness sintered body such cermet (for example, WCxe2x80x94Co), PCD or polycrystalline cubic boron nitride (PcBN) with a high toughness sintered body having a composition different from that of the core material, and thus the fracture resistance of the construction is increased to enhance the toughness without lowering the hardness. However, in the composite construction described in U.S. Pat. No. 6,063,502, in case the component, which is finally converted into a bonding phase as a result of the appearance of a liquid phase, exists in the core material and/or the shell layer, the liquid phase diffuses toward the core material and the shell layer. As a result, the core material has the same characteristics as those of the shell layer and thus the effect of improving the toughness disappears. In case the sintering temperature of the core material drastically differs from that of the shell layer, there was a problem that the liquid phase component moves from the portion having a high sintering temperature to the portion having a low sintering temperature and the portion having a low sintering temperature can not be densificated, an thus a large number of holes (voids) are remained.
A main object of the present invention is to provide a composite construction which has both high hardness and high toughness.
Another object of the present invention is to provide a composite construction which can easily attain desired characteristics.
(First Composite Construction of the Present Invention)
The present inventors have found that, when using PCD as a core material, a difference in thermal expansion coefficient between PCD and a sintered body as a shell layer, can be reduced by controlling an amount of an iron group metal in PCD to the amount larger than that in the shell layer, and thus obtaining a composite construction which has both high hardness and high toughness.
The composite construction of the present invention is characterized by a composite construction comprising a continuous core material made of PCD obtained by bonding diamond particles with an iron group metal; and a shell layer made of a sintered body obtained by bonding at least one kind of hard particles, which are selected from the group consisting of carbides, nitrides and carbonitrides of at least one kind of metal elements (M) selected from the group consisting of metals of Group 4a, 5a and 6a of the Periodic Table, with an iron group metal, the outer periphery of the core material being coated with the shell layer; wherein an amount of the iron group metal in the core material is larger than that of the iron group metal in the shell layer.
(Second Composite Construction of the Present Invention)
Also the present inventors have found that, by providing an intermediate layer capable of preventing infiltration or diffusion of a bonding phase between a core material and a shell layer of a construction, the compositions of the core material and the shell layer can be easily controlled and a sound fine sintered body free from pores can be manufactured, and thus obtaining a composite construction which can easily attain desired characteristics such as high hardness and high toughness.
The composite construction of the present invention comprises a continuous core material; and a shell layer having a composition different from that of the core material, the outer periphery of the core material being coated with the shell layer; wherein at least one of the core material and the shell layer is made of a sintered body obtained by bonding crystal grains with a bonding phase and at least one intermediate layer, which has a region in which the content of the bonding phase gradually decreases toward the inside from at least one of the core material and the shell layer, is provided between the core material and the shell layer.
Other objects and advantages of the present invention will become apparent from the following detailed description.